A delta motor system typically includes a delta motor, a three phase power source, a fault contactor and a motor controller. During start up, delta motors often experience potentially damaging high inrush currents and starting torques. This can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. In addition, current peaks during motor startup can also cause voltage disturbances in the power supply.
Motor controllers are typically used to restrict the motor torque and reduce the high starting currents by controlling the application of voltage from the three phase power source to the delta motor. The motor controller generally includes a set of three control switches that are connected between the line voltage terminals of the three phase power source and the windings of the delta motor. The motor controller regulates the voltage from the three phase power source to the delta motor by selectively opening and closing the three control switches. The proper operation of the delta motor is dependent on the proper regulation of the control switches.
The fault contactor is commonly used to disconnect the three phase power source from the delta motor in the event that the delta motor system malfunctions. The fault contactor includes a set of three contacts that are also connected between each of the delta motor windings and the line voltage terminals. Each of the delta motor windings are intended to receive the fault contact connection on one side and the control switch connection on the other side. Alternatively, the fault contactor function can also be done with a shunt trip circuit breaker, an in-line contactor, or fuses.
The motor controller's internal timing mechanisms are specifically designed to regulate the application of specific line voltages from the three phase power source to specific delta motor windings based on a predesignated wiring configuration. Conventional electrical leads are typically used to connect the delta motor windings to the control switches and to the fault contacts. Since the electrical leads providing connection to the delta motor terminals are not always clearly marked, mistakes in wiring the delta motor system are common. Some of the most common wiring errors involve a single dead ended motor winding, three dead ended windings and swapping the delta motor connections to the motor controller with the delta motor connections to the fault contactor.
A wiring configuration includes a single dead ended winding when the two leads providing connection to a single winding are electrically coupled to a single line voltage terminal while the other two windings are connected in parallel across the remaining two line voltages terminals. In this configuration, the dead ended winding does not have any current flowing through it while the other two windings are subjected to lower motor torque and significantly higher current conditions. The lower motor torque in combination with the higher operating current can potentially damage both the delta motor and the motor controller.
When each of the three line voltage terminals of a three phase power source have been connected such that both ends of each motor winding are connected to the same line voltage terminal, the windings are incorrectly wired in a dead ended winding configuration. When a run command is issued to a delta motor having all of its windings in a dead ended configuration, the indicator for the motor controller will show that it is running and the indicator for the delta motor will show that the delta motor is up to speed even though the delta motor has not actually started and there is no current flowing through the windings.
Finally the third wiring error occurs when the delta motor terminals designated for connection to the motor controller control switches are connected to the fault contacts and the motor terminals designated for connection to the fault contacts are connected to the control switches. In this wiring configuration, the phase shift in the currents through each of the windings are no longer compatible with motor controller's internal mechanisms and although the delta motor will run, the motor controller will be unable to perform its necessary current limiting functions during start up or will be unable to supply full voltage to the motor for operation after starting.
Clearly it would be desirable to use a motor controller that automatically detects a fault condition if the motor system has been incorrectly wired having a single motor winding configured in a dead ended configuration or having all three of the motor windings configured in a dead ended configuration or if the delta motor connections to the fault contactor and to the motor controller have been swapped. Detecting these fault conditions prior to operating the delta motor enables the user to correct the faulty wiring prior to subjecting the delta motor and the motor controller to potentially damaging overcurrent and low motor torque conditions. In addition, automatic detection of these faults reduces troubleshooting time and associated expenses. The present invention seeks to achieve these objectives.